1. Field of the Invention
The present invention relates generally to a microstrip antenna for use on a weapons system to receive externally generated data. More specifically, the present invention relates to a reduced size GPS conical shaped microstrip antenna array which receives GPS data and which is adapted for use in a small area on a weapons system such as a missile.
2. Description of the Prior Art
There is currently a need for a miniature microstrip antenna array which receives GPS (Global Positioning System) data for use in a confined area within a small diameter weapons system such as a missile, a artillery shell, smart bomb or the like. The microstrip antenna array needs to operate at the GPS L1 Band centered at a frequency of 1.575 GHz, have a bandwidth of twenty megahertz and right hand circular polarization. The shape of the microstrip antenna array should ideally be conical.
A microstrip antenna array has a unique problem in that the feed line for each antenna element becomes effectively connected to the antenna element as the feed line is positioned closer to the element. The feed line no longer distributes antenna power to the antenna elements in phase and amplitude due to coupling between the antenna elements and the feed line.
In the past microstrip antenna arrays have been designed with considerable separation between the feed line and the antenna elements so that coupling was not a concern to the antenna designer. When less space was available, multiple dielectric layers were used for the antenna and the feed line was placed on a lower dielectric layer within the antenna. This allows the feed line to be made smaller with a resulting reduced spacing to the antenna elements.
However, there is still a need to minimize the interaction between the feed line for the antenna and the microstrip antenna elements of the antenna when the antenna is confined to a very small area and the designer needs to place the feed on the same dielectric layer as the antenna elements of the antenna.